Polypeptides. Part XXIV. Synthesis of isariic acid

Abstract

L- and D-3-Hydroxydodecanoylglycyl-L-valyl-D-leucyl-L-alanyl-D-valine (IV) and their methyl esters have been synthesised. The compounds derived from the D-hydroxy-acid were indistinguishable from isariic acid and methyl isariate; this confirmed the amino-acid sequence of isariin, a metabolite of Isaria cretacea which liberates isariic acid on alkaline hydrolysis. Predictably, attempts to cyclise the hexapeptide (IV) were unsuccessful; this can be attributed to the presence of the C-terminal valine residue.